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平狄克,魯賓費爾德微觀經濟學第四版PPT教案3_圖文

平狄克,魯賓費爾德微觀經濟學第四版PPT教案3_圖文

微觀經濟學
(平狄克,魯賓費爾德,第四版)
LECTURE 3 消費者理論

1

一、消費者行為

2

基本概念
市場籃子、無差異曲線、無差異曲線圖、 邊際替代率、效用、基數效用函數和序 數效用函數、預算約束、預算線、拐點 解、顯示性偏好、邊際效用、消費者物 價指數(CPI)、拉氏指數、派氏指數、 連鎖權重物價指數 消費者行為研究的三個步驟:
消費者偏好-預算約束-結合前面二者確定消 費者選擇
3

消費者偏好
基本假設: 偏好的完全性、可傳遞性,以及“多總比少好”。 無差異曲線的特征: 向下傾斜 其右上和左下分別表示偏好于和不偏好于 每條無差異曲線絕不相交 邊際替代率(無差異曲線的斜率)遞減(無差異曲 線是凸的)。 完全替代品和完全互補品,圖PP5,6。 思考:BADS,無差異曲線將是怎么樣的? 序數排列就足以解釋大多數消費者決策是如何做出的。
4

Consumer Preferences
Apple Juice (glasses) 4

Perfect Substitutes

3

2

1
Orange Juice (glasses)
5

0

1

2

3

4

Consumer Preferences
Left Shoes

4

3

Perfect Complements

2

1

0

1

2

3

4

Right Shoes
6

預算約束
預算線的斜率反映了兩種商品的相對價格,是 兩種商品價格比取負;截距表示使用已有收入 能夠購買的最多單種商品。 收入變化:
收入增加/減少使預算線向外/內平移。圖PP8;

價格變化:
一種商品價格變化,預算線以另一種商品的截距點 為原點旋轉。圖:PP9; 兩種商品價格發生同比變化,預算線斜率不變,向 外或向內平移。
7

Budget Constraints
Clothing (units per week)

80

A increase in income shifts the budget line outward

60
A decrease in income shifts the budget line inward
L3 (I = $40) L1 (I = $80) L2 (I = $160)

40

20
0

Food
(units per week)
8

40

80

120

160

Budget Constraints
Clothing (units per week) An increase in the price of food to $2.00 changes the slope of the budget line and rotates it inward. A decrease in the price of food to $.50 changes the slope of the budget line and rotates it outward.

40

L3
(PF = 2)
40

L1
(PF = 1)
80

L2
120 160

(PF = 1/2)
Food
(units per week) 9

消費者選擇
最大化消費者滿足的市場籃子必須具備兩個條 件:
應在預算線上, 應給予消費者最受偏好的商品和勞務組合。

根據無差異曲線的斜率MRS=-?C/?F,預算線 斜率為-Pf/Pc,最大化條件是MRS=Pf/Pc 因此,當邊際替代率等于兩種商品價格比時, 消費者獲得最大滿足。圖 PP11。 拐點解:
發生在無差異曲線與橫軸或縱軸相切時,此時 MRS≠Pa/Pb。圖 PP12。
10

Consumer Choice
Clothing (units per week)

Pc = $2

Pf = $1

I = $80
At market basket A the budget line and the indifference curve are tangent and no higher level of satisfaction can be attained.

40

30 A 20

At A: MRS =Pf/Pc = .5

U2
Budget Line 0 20 40 80 Food (units per week)
11

A Corner Solution
Frozen Yogurt (cups monthly)

A U1 U2 U3

A corner solution exists at point B.

B

Ice Cream (cup/month)
12

邊際效用與消費者選擇
邊際效用遞減法則 相等邊際原則:
? 邊際效用與無差異曲線: (?C / ?F ) = MU F / MU C 又,在無差異曲線上:MRS=-?C/?F 因此 MRS = MU F/MU C 又根據消費者最大化其滿足感時有MRS=Pf/Pc 因此有效用最大化條件(相等邊際原則):

MU F/MU C = P F/P C
13

生活成本指數
拉氏指數VS派氏指數:
兩種指數都涉及基期和當前的價格水平對比; 拉氏指數立足于基期消費構成,派氏指數立 足于當前消費構成; 拉氏指數傾向于高估生活成本,派氏指數傾 向于低估生活成本。

14

二、個體需求和市場需求

15

個體需求
需求曲線的兩個特點:
沿曲線移動時可獲得的效用發生變化; 曲線上的每點消費者都是通過實現兩種商品的邊際替 代率等于其價格比來實現效用最大化的。

收入-消費曲線
描畫出與每種收入水平相聯系的效用最大化商品組合。 收入增/減將使預算線右/左移,并使消費點沿收入-消 費曲線右/左移;同時使需求曲線右/左移。 當收入-消費曲線有正的斜率時,需求隨收入增加而增 加,需求的收入彈性為正,此種商品為正常商品; 當收入-消費曲線有負的斜率時,需求隨收入增加而減 少,需求的收入彈性為負,此種商品為劣質商品。
16

An Inferior Good
Steak15 (units per month)
C Income-Consumption Curve Both hamburger and steak behave as a normal good, between A and B...

10
U3

5

B

U2 A U1

…but hamburger becomes an inferior good when the income consumption curve bends backward between B and C.

5

10

20

Hamburger 30 (units per month)
17

個體需求
恩格爾曲線:
將商品的消費量與收入聯系起來。 正常商品的恩格爾曲線向上傾斜; 劣質商品的恩格爾曲線則向下傾斜。

18

Engel Curves Income
($ per month) 30

Inferior 20
Engel curves slope backward bending for inferior goods.

Normal 10

0

4

8

12

16

Food (units per month)
19

個體需求
替代品VS互補品 替代品 互補品
一種商品價格上漲/下跌導致另一種商品需求上升/ 下降,這兩種商品是替代品; 一種商品價格上漲/下跌導致另一種商品需求下降/ 上升,這兩種商品是互補品。 價格消費曲線如向下傾斜,則兩種商品被視為替代 品;該曲線向上傾斜,則兩種商品被視為互補品; 值得注意的是,兩種商品可能在一定條件下是前者, 一旦條件改變(如收入變化)則變成后者。

20

替代品VS互補品 替代品 互補品
Clothing (units per month) A-B,替代品;B-D,互補品 替代品; 替代品 互補品

6 5 4

A
U1

Price-Consumption Curve
D B U3

U2

4

12

20

Food (units per month)
21

個體需求
替代效應與收入效應: 替代效應與收入效應
替代效應:在效用保持恒定的條件下因一種商品價 格變化而改變對該種商品的消費數量,一般是價格 下跌,消費數量增加。 收入效應:在價格水平保持恒定的條件下因購買力 變化而改變對該種商品的消費數量,收入增加,對 某種商品的消費可能上升或下降。 即便是劣質商品,收入效應也很少有可能大于替代 效應。 吉芬商品:收入效應大于替代效應,導致對某種商 品的需求曲線向上傾斜。
22

Income and Substitution Effects: Normal Good
Clothing (units per month) R
When the price of food falls, consumption increases by F1F2 as the consumer moves from A to B. The substitution effect,F1E, (from point A to D), changes the A relative prices but keeps real income (satisfaction) constant. The income effect, EF2, ( from D to B) keeps relative prices constant but increases purchasing power.

C1

D C2
Substitution Effect

B

U2 U1
E S F2
Income Effect

O

F1

Total Effect

T

Food (units per month)
23

Income and Substitution Effects: Inferior Good
Clothing (units per month) R
Since food is an inferior good, the income effect is negative. However, the substitution effect is larger than the income effect.

A B

D

U2

Substitution Effect

U1
E S F2 T
Food (units per month)
24 Income Effect

O

F1
Total Effect

市場需求
市場需求曲線:
更多消費者進入市場將使市場需求曲線右移; 影響眾多消費者需求的因素也將影響市場需 求。
E 需求的價格彈性: P =

需求的點彈性: EP = (P/Q)(1/slope) 需求的弧彈性: EP = ( ?Q/?P)( P / Q)

?Q/Q ?Q / ?P = ?P/P Q/ P

消費者剩余:圖PP26
25

Consumer Surplus
Price
($ per ticket)

20 19 18 17 16 15 14 13
Actual Expenditure Consumer Surplus

Consumer Surplus for the Market Demand

1/2x(20 ? 14)x6,500 = $19,500

Market Price

Demand Curve

0

1

2

3

4

5

6

Rock Concert Tickets
26

市場需求
連帶外部效應:
攀比效應:
原因:互相攀比,趕時髦。 圖 PP28-31.

虛榮效應:
原因:物以稀為貴。 圖 PP32-33.

27

Positive Network Externality: Bandwagon Effect
Price
($ per unit)

D20

D40 D60 D80 D100

When consumers believe more people have purchased the product, the demand curve shifts further to the the right .

Quantity

20

40

60

80

100

(thousands per month) 28

Positive Network Externality: Bandwagon Effect
Price
($ per unit)

D20

D40 D60 D80 D100

The market demand curve is found by joining the points on the individual demand curves. It is relatively more elastic.

Demand

Quantity

20

40

60

80

100

(thousands per month) 29

Positive Network Externality: Bandwagon Effect
Price
($ per unit)

D20

D40 D60 D80 D100

$30

Suppose the price falls from $30 to $20. If there were no bandwagon effect, quantity demanded would only increase to 48,000

$20

Demand
Pure Price Effect

20

40

48 60

80

100

Quantity
(thousands per month) 30

Positive Network Externality: Bandwagon Effect
Price
($ per unit)

D20

D40 D60 D80 D100

$30

But as more people buy the good, it becomes stylish to own it and the quantity demanded increases further.

$20

Demand
Pure Price Effect

Bandwagon Effect 20 40 48 60 80
100

Quantity
(thousands per month) 31

Negative Network Externality: Snob Effect
Price
($ per unit)

Demand

$30,000

Originally demand is D2, when consumers think 2000 people have bought a good.

However, if consumers think 6,000 people have bought the good, demand shifts from D2 to D6 and its snob value has been reduced.

$15,000

D2 D4
D8 2 4 6 8 D6 Quantity 14
per month) 32 (thousands

Pure Price Effect

Negative Network Externality: Snob Effect
Price
($ per unit)

Demand

$30,000

The demand is less elastic and as a snob good its value is greatly reduced if more people own it. Sales decrease as a result. Examples: Rolex watches and long lines at the ski lift.

Net Effect $15,000

Snob Effect

D2 D4
D8 2 4 6 8 D6 Quantity 14
per month) 33 (thousands

Pure Price Effect

三、不確定條件下的選擇

34

描繪風險
正確計量風險必須了解:
行為可能導致的所有結果, 每種結果發生的概率。

主觀判斷VS客觀判斷 VS 幾個基本概念:
期望值: E(X) = Pr1X1 + Pr2 X 2 + ... + Prn X n 方差 標準差:σ = Pr1[X1 ? E( X )2 ] + Pr2 [X 2 ? E( X )2 ]
35

風險的偏好
預期效用:
是各種結果根據發生概率進行加權的平均。

風險規避VS風險中性VS風險偏好
風險規避:
收入帶來的邊際效用遞減的個體是風險規避型的; 對保險的運用體現了風險規避行為; 例子:PP37-42

風險中性: 圖PP43; 風險偏好: 圖PP44.
36

一個例子
Risk Averse

A Scenario
A person can have a $20,000 job with 100% probability and receive a utility level of 16. The person could have a job with a .5 chance of earning $30,000 and a .5 chance of earning $10,000.

37

一個例子
Risk Averse

Expected Income = (0.5)($30,000) + (0.5)($10,000) = $20,000

38

一個例子
Risk Averse

Expected income from both jobs is the same -- risk averse may choose current job

39

一個例子
Risk Averse

The expected utility from the new job is found:
E(u) = (1/2)u
($10,000)

+ (1/2)u

($30,000)

E(u) = (0.5)(10) + (0.5)(18) = 14
E(u) of Job 1 is 16 which is greater than the E(u) of Job 2 which is 14.
40

一個例子
Risk Averse

This individual would keep their present job since it provides them with more utility than the risky job. They are said to be risk averse.

41

一個例子
Utility 18 16 14 13 B A 10 D C E
The consumer is risk averse because she would prefer a certain income of $20,000 to a gamble with a .5 probability of $10,000 and a .5 probability of $30,000.

0

10

15 16 20

30

Income ($1,000)
42

Risk Neutral
E

Utility

18

C

12

The consumer is risk neutral and is indifferent between certain events and uncertain events with the same expected income.

A

6

0

10

20

30

Income ($1,000)
43

Risk Loving
Utility 18 E
The consumer is risk loving because she would prefer the gamble to a certain income.

8 A 3 0 10

C

20

30

Income ($1,000)
44

風險的偏好
風險溢價:
結果可能的變動越大,風險就越大,風險溢 價也越大。 例:PP46-51.

45

風險溢價舉例
A Scenario
The person has a .5 probability of earning $30,000 and a .5 probability of earning $10,000 (expected income = $20,000). The expected utility of these two outcomes can be found:
E(u) = .5(18) + .5(10) = 14

Question
How much would the person pay to avoid risk?

46

風險溢價舉例
Utility Risk Premium
Here , the risk premium is $4,000 because a certain income of $16,000 gives the person the same expected utility as the uncertain income that has an expected value of $20,000.

G
20 18 14

E C A F

10

0

10

16

20

30

40

Income ($1,000)
47

風險溢價舉例(續)
Variability in potential payoffs increase the risk premium. Example:
A job has a .5 probability of paying $40,000 (utility of 20) and a .5 chance of paying 0 (utility of 0).

48

風險溢價舉例(續)
Example:
The expected income is still $20,000, but the expected utility falls to 10. Expected utility = .5u($) + .5u($40,000) = 0 + .5(20) = 10

49

風險溢價舉例(續)
Example:
The certain income of $20,000 has a utility of 16. If the person is required to take the new position, their utility will fall by 6.

50

風險溢價舉例(續)
Example:
The risk premium is $10,000 (i.e. they would be willing to give up $10,000 of the $20,000 and have the same E(u) as the risky job.

51

風險的偏好
將預期收益和收益的標準差作為兩軸可 畫出無差異曲線。
風險的規避程度可通過圖形直觀觀察:圖 PP53-54.

52

Risk Aversion and indifference Curves
U3
Expected Income

U2 U1

Highly Risk Averse:An increase in standard deviation requires a large increase in income to maintain satisfaction.

Standard Deviation of Income
53

Risk Aversion and Indifference Curves
Expected Income Slightly Risk Averse: A large increase in standard deviation requires only a small increase in income to maintain satisfaction.

U3 U2 U1

Standard Deviation of Income
54

降低風險
降低風險的三種方式:
多樣化、保險、信息搜集

多樣化:
不要把雞蛋放在一個籃子里,例:課本

保險:
購買保險通過放棄一定的預期收益來增加確定性 , 完全保險:保險成本等于預期損失。 單起事件是隨機發生和不可預測的,但眾多相似事件 的平均結果則可根據大數法則進行預測。

信息的價值:
信息是否完全決策的預期結果將大相徑庭。例:課本
55


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